The erythrocyte sedimentation rate (ESR) is a laboratory test that measures the distance, in millimeters, that erythrocytes fall in anticoagulated blood in one hour. It was introduced by Fahraeus in 1918, and has become one of the routine blood examinations in many hospital laboratories since then. The red blood cells (RBCs) are known to possess a net negative charge, the zeta potential, which slows down the sedimentation of RBCs when they are suspended in normal plasma. Alterations in the composition of plasma will reduce the zeta potential and induce aggregation and rouleaux formation of the RBCs, and their rate of sedimentation will then be increased. Plasma composition changes follow many tissue damage, inflammation and other pathological processes. Measuring ESR can, therefore, provide clinicians with information about underlying diseases. Three types of information can be obtained by means of ESR test: (I) to determine the presence or abscence of disease; (II) to monitor the progression of an already recognized disease; (III) to measure the response to therapy. For instance, congestive heart failure, polycythemia and use of anti-inflammatory agents etc., are known to cause low ESR, whereas various types of infection, malignancy, collagen vascular diseases, and a variety of medications such as heparin, oral contraceptives etc., can cause elevated ESR. Of particular importance is the predictive value of markedly elevated ESR, values greater than 100 mm per hour. It is noted that a patient found to have a markedly elevated ESR has a 95 percent likelihood of an infectious, inflammatory, collagen vascular or neoplastic process. Further investigation is warranted for such patients. ESR is, therefore, useful as a "sickness index", or a "broad spectrum indicator" of disease.
Many methods have been used to measure ESR. The earliest one is that of Westergren (as shown in FIG. 1), introduced into medicine in 1921, which is still considered the standard method of measuring ESR. With the Westergren method, the anticoagulated blood is filled into a 300 mm long Westergren glass tube to the zero mark located 200 mm from below. The glass tube is set up vertically and left undisturbed for one hour. The distance from the junction of plasma and RBC column to the zero mark after one hour is the ESR desired. The second most popular method is due to Wintrobe and Landsberg (as shown in FIG. 2), introduced in 1935. This method is performed with a 120 mm long tube whose internal diameter is 2.5 mm, the same as that of the Westergren tube. The procedure is similar to that of the Westergren method. In 1972, Bull and Brailsford devised another method called Zeta Sedimentation ratio (ZSR) that is unaffected by anemia and responds in a linear fashion to an increase in plasma fibrinogen or gamma globulin level. The ZSR is measured by using an apparatus named Zetafuge (as shown in FIG. 3) that can produce low-speed centrifugation to speed the sedimentation process. The ZSR technique eliminates some disadvantages of ESR, but unfortunately does not meet with wide acceptance.
Both the Westergren and Wintrobe-Landsberg methods, or minor modifications of them, are manually operated, and are therefore labor-requiring and subject to technical error. Long term observation of ESR with these methods are also impractical. No automated monitoring, recording device of ESR is available except a photographic method, devised by King et al in 1981 (as shown in FIG. 4), which is still a primitive one piece of in that only one data at one particular time is obtainable. To facilitate detailed recording of ESR, mass screening, statistical analysis, and further study into the obscure nature of erythrocyte sedimentation, the undersigned inventors have developed this automatic monitoring and recording unstrument of erythrocyte sedimentation process.